1. Field of the Invention
This invention relates to a web material folding device wherein a web material made of a plastics film or the like is folded by a predetermined length into a Z-shaped manner.
2. Description of the Prior Art
Recently, plastics bags have been used in large quantities as packaging materials because of being sanitary and suitable for mass production at low cost. Furthermore, there has been proposed that a continuous material of the above-described plastics bags (hereinafter referred to as a "plastics continuous bag-shaped material" or simply as a "continuous bag-shaped material") is folded into a Z-shaped manner, housed in a cardboard box and the plastics bag can be taken out as necessary in the same manner as in the pop-up take-out method of tissue paper, one bag after another (Japanese Patent Kokai "Laid-Open" Nos. 96948/82, 142872/82, U.S. patent application Ser. No. 315,815 and Japanese Patent Application No. 194004/81).
Now, as a device for folding the aforesaid plastics continuous bag-shaped material into a Z-shaped manner, there has been proposed such a device wherein there are used two cylindrical rolls each provided on the peripheral surface thereof with an attracting surface within a predetermined angle and the continuous bag-shaped material is alternately folded by means of the attracting surfaces of these two rolls (Japanese Utility Model Kokai "Laid-Open" No. 49327/79). However, this proposal is disadvantageous in that the folding operation is low in reliability. Furthermore, to obviate the above disadvantage, there has been proposed to provide two prismatic attracting members each having two attracting surfaces in such a manner that these attracting surfaces are opposed to each other, whereby these two attracting surfaces are caused to fall toward the opposed ones, to thereby effect the folding operation (Japanese Patent Kokai "Laid-Open" No. 107364/82). However, the latter device as well as the former device using the rolls are adapted to effect the folding operation by use of the vacuum attraction and the release therefrom, and hence, the proposals are disadvantageous in that an installation of a vacuum pump, etc. is required, the devices are rendered large-sized and expensive in cost, and further, not suitable for high folding speed.
In view of the above problems, as a device capable of reliably and efficiently folding a web material without needing to use a large-sized apparatus such as a vacuum pump, there has been proposed a device wherein the web material is alternately guided around the forward end edges of a pair of thin plates alternately reciprocating toward a folded end portion in the longitudinal direction of the web material to thereby fold the web material (Japanese Patent Application No. 128496/81). However, in the thus proposed device, operations of the thin plates contacting the web material are so frequent that the web material tends to be damaged, and further, a stabilized folding operation at high speed cannot be expected to a satisfactory extent.
Further, there have been proposed various stackers in each of which the web material, which has been folded by a folding machine, is reliably piled up and supported (Japanese Utility Model Kokai "Laid-Open" No. 151206/82, Patent Kokai "Laid-Open" Nos. 137264/82 and 151335/82, and Patent Application No. 128496/81). However, each of the proposed stackers is constructed such that a receiving bed on which the folded web material is piled up is pressed down to be gradually depressed as the quantity of the folded web material increases. With this arrangement, sections of the folded web material piled up on the receiving bed are pressed down and closely adhered to one another, thus presenting the disadvantages that wrinkles tend to occur and the subsequent handling of the web material becomes not necessarily easy. Further, it has been difficult to take out a predetermined number of sections of the folded web material during folding operation, and moreover, also difficult to automate the processes from an operation of folding the web material to an operation of packaging the folded web material. Furthermore, the receiving bed is constructed to be pressed downwardly with the increase in the quantity of the folded web material. Consequently, an additional force is applied to the web material folded and piled up in a large quantity on the receiving bed, thus presenting the disadvantage that, when a large quantity of the folded web material is stacked on the receiving bed, the piling of the folded web material may collapse.